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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 02-27-12, 03:51 PM   #26
rhino919
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I just did some napkin math - 100% of inseam = distance from pedal spindle to top of seat. I figure with knee slightly bent, the height of the shoe is washed out, and honestly I just wanted to put some numbers "on paper" to drive the discussion (which thankfully you've confirmed that you thought through).
Yes, I've spent lots and lots and lots of time thinking about this design. My wife says I am obsessed! Thanks for asking questions to keep moving the discussion forward.

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With this design, I'd suggest you CONFIRM that your desired seatpost can be that high, maybe even check to see if there's an alternate product on the market that also can be that high. If you're doing a custom tandem that could last 20 years, you don't want to end up with a design that snaps seatposts (and just in case it does, you want to have a different product to use instead).
Confirmed - We will have approximately 300mm of seatpost showing which leaves another 30mm to the min. insertion line. Of course we also have to make sure that the seatpost extends below the junction of the top tube and seat tube. There are several other options for 400mm+ seatposts - Thompson (410mm), Easton EC70/90 (400mm), BBB Longscraper (450mm). Since my wife only weighs 125-130lbs we can generally use anything we want for her without worrying about breakage. On our singles, her chains and tires last at least twice as long as mine.

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My only thought then would be to rotate your stoker "up" - pull the stoker saddle back perhaps 3", then bring the stoker bars up the proportionate amount, and you may then be able to shorten the stoker box AND give her more ability to see over/around you.
We started with a position something more like what you describe on our Cannondale, and have migrated away from it. Even when she takes her hands off of the bars and sits upright, she really can't see over/around me. In the end, the position shown is what she has asked for. And we all know, what the stoker wants is what the stoker gets

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Old 02-27-12, 03:54 PM   #27
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Rhino919: did I read your post correctly in that the ti tubes will be coupled to the steel tubes?
I think I have answered this in my response to StanleyJ. If it still doesn't make sense, let me know and I will try to describe better
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Old 02-27-12, 04:19 PM   #28
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Great to have people trying new things. Keep us informed.
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Old 02-27-12, 04:25 PM   #29
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I would prefer a longer seat tube for the stoker. Mainly because I think it would look better. Looong seat posts look a bit like they should be on a mountain bike rather than a road bike to me.
I actually prefer the highly sloped TT design with a long seatpost, but appreciate that there are many that don't. I would guess that there will be those that look at the final product and think how much better it could have been if they had just......

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Also unsure about having your top tube length so that you need a 130mm stem. I guess it is ok if you are absolutely sure on the positioning, but if you decided to move your saddle back a bit or just wanted a bit more reach it doesn't give you much room to move as far as getting a longer stem.
Good comment! I've spent some hours "agonizing" over this decision and hope that I have gotten it right. One advantage of a tandem is that you can use a long stem without worry for overloading the front wheel. If anything, I would expect to shorten my reach rather than lengthen it as my body ages.
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Old 02-27-12, 04:56 PM   #30
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rhino--that's gonna be pretty darned cool if it works as intended. I'll wait to see photos before asking how the clamps will be made and oriented or other such details. Pics are worth a lotta words. As odd as it otherwise sounds, it's almost like you could "tune" your ride depending on whatever tube you felt like sliding in there. Cool concept. Do the clamps have an expected lifecycle of opening/tightening?

some of english's bikes are really far out there, but he's not afraid to take things on and redefine the "norm." plus, it sounds like he's got the riding & racing chops that lend a lot of credibility. it's fun to watch what he does. lots of posts over on the ww forum of his creations.

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You can see pictures of the tube in socket method applied to a recumbent tandem here. Bike Friday also uses this design on their tandems.

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Old 02-27-12, 06:46 PM   #31
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Do the clamps have an expected lifecycle of opening/tightening?
I would expect the life cycle to be infinite. I don't see how it would be any different than the seatpost clamp on a steel frame.
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Old 02-28-12, 09:29 AM   #32
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How do your hips/quads fit between such a narrow stoker bar? Our stoker bar is a 46mm deda (outside to outside), and I still get the occasional rub passed her hands when she is using the stoker hoods. I am not a big guy, tall nor wide..

Only caveat would be if the stoker stem is long enough to put her bars entirely behind you. Perhaps that is the case?
Pay attention to this posting by uspspro. Your stoker might like 40cm bars, but your legs will probably hit them and make the setup unrideable (and see you are planning on using a 13cm stoker stem, so I don't think the bars will be far enough back to get them out of your way). Like uspspro, we run a 46 cm stoker bar, with an 18cm stoker stem, and I brush her hands with my thighs when she is on the outside of the bars.
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Old 02-28-12, 09:52 AM   #33
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Pay attention to this posting by uspspro. Your stoker might like 40cm bars, but your legs will probably hit them and make the setup unrideable (and see you are planning on using a 13cm stoker stem, so I don't think the bars will be far enough back to get them out of your way). Like uspspro, we run a 46 cm stoker bar, with an 18cm stoker stem, and I brush her hands with my thighs when she is on the outside of the bars.
We use a 44cm stoker bar and a 18cm stoker stem with a good upslope so effective length is less. Originally this put her bars right behind the top of my saddle with just enough room for her to grip the bars. Since that time have have migrated to about 15-20mm less seat setback and now she has more room. I am 5'9" and 150 lbs.

There does need to be enough room for the stoker to grip the hoods so she will need clearance for thumbs between her bars and your hips so measure carefully. On the other hand if you measured carefully and 40cm fits then great.

Did you consider S&S with Ti middle tubes and decided against it due to the cost?

Wayne
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Old 02-28-12, 10:19 AM   #34
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Pay attention to this posting by uspspro. Your stoker might like 40cm bars, but your legs will probably hit them and make the setup unrideable (and see you are planning on using a 13cm stoker stem, so I don't think the bars will be far enough back to get them out of your way). Like uspspro, we run a 46 cm stoker bar, with an 18cm stoker stem, and I brush her hands with my thighs when she is on the outside of the bars.
Hmm, I thought I had answered this twice before, but obviously I need to do better with my explanations since it keeps coming up. Our current tandem has 38cm stoker drop bars mounted with a 110mm stem. My stoker dislikes the shape/feel of the cane creek dummy levers, so I made a set of round stoker pegs. With this setup, my leg will occasionally brush the stokers hands. With the new tandem we are using a 130mm stem which will give more clearance. However, the bars will be higher up than on the Cannondale. This will again bring the bars closer to my abnormally narrow hips (33cm out to out). If this does prove to be a problem, changing the stoker bar and/or stem will be very easy. Hope this clarifies things!
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Old 02-28-12, 11:16 AM   #35
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We have a 14cm stoker stem and 40cm stoker setup and it works fine. I have minimal brushup and it is not a problem at all. She did have a 38cm width and that proved troublesome. We ended up putting the 38cm on her single bikes and 40cm on tandem. It all worked out just like it will for rhino919.
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Old 02-28-12, 04:09 PM   #36
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Did you consider S&S with Ti middle tubes and decided against it due to the cost?
At $1,300 to $2,500 to add them, S&S couplers wouldn't have fit in the budget. However, if there was no additional cost for the S&S, I would still choose the English method, as I think it is a more elegant solution.
1) It allows for easily changing to different tube materials or thicknesses, although you could argue that a correctly designed frame shouldn't need this option.
2) It eliminates the eccentric BB. To tension the timing chain you clamp the top tube and one end of the boom tube in place, push down on the seat to tension the chain, and clamp the other end of the boom tube.

I do see some potential issues that may not make it suitable for everybody.
1) The clamp bolts must be torqued correctly to make sure the tubes don't slide while riding.
2) The tension of the chain will vary depending on how hard you push down on the seat.
3) The length of the bike could vary a little (+/- 1mm?) from assembly to assembly which would require adjustments to the derailleurs.

At this point, I'm perfectly happy to deal with these issues. Once I actually get the bike, my opinion may change.
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Old 02-29-12, 07:16 AM   #37
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At $1,300 to $2,500 to add them, S&S couplers wouldn't have fit in the budget. However, if there was no additional cost for the S&S, I would still choose the English method, as I think it is a more elegant solution.
1) It allows for easily changing to different tube materials or thicknesses, although you could argue that a correctly designed frame shouldn't need this option.
The ability to substitute tubes of different characteristics is very appealing. I now ride a tandem that is the result of some less elegant experimentation along that line. Given the many factors involved, including personal preference, it seems unlikely to me that even a very talented builder can somehow design a perfect frame for a team on the first attempt. I believe we have arrived at a good fit for us but your tandem will allow for much more tuning of the frame limited only to your pocket book and patience.

Wayne
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Old 03-06-12, 09:28 AM   #38
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Please keep us updated - I think this sounds like a really cool build, and I like the idea that you could swap the pipes to improve stiffness or ride. Re-setting the RD tension is no big deal, since you'd have the allen keys out anyway to rebuild the bike after flying or similar.
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Old 03-06-12, 10:33 AM   #39
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"You can see pictures of the tube in socket method applied to a recumbent tandem here. Bike Friday also uses this design on their tandems."

To be pedantic, while English is his own project, in effect he's also a major part of Bike Friday. I.E. I'd say that he's using the bikefriday design, not the other way around.

Last edited by CaptainHaddock; 03-06-12 at 10:33 AM. Reason: making quote clearer
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Old 03-06-12, 11:37 AM   #40
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Ask your builder to check the boom tube length relative to where the front bottom bracket spindle will fall in the eccentric once the sync chain is installed.

I believe he may want to add or subtract about 1/2 and inch from that 31" C-T-C spec so your spindle will fall more in the middle vs. being biased well forward or well back of center.

If he keeps it at 31", you can adjust it back to center with a half-link in your sync chain, or you can bias your saddle fore-aft to adjust set-back and then establish your stem length for reach once you've got your set-back squared away.

This is why you'll find that most production tandems use the 1/2" spec on their boom tubes, e.g., 28.5" for Co-Motion, 27.5" for Santana, 28.6" for Cannondale, etc...
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Old 03-06-12, 11:51 AM   #41
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That's actually a very important point, something I'd have never thought of when I had mine built. (Thanks TG and others for your tips in that regard on my build thread).

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Ask your builder to check the boom tube length relative to where the front bottom bracket spindle will fall in the eccentric once the sync chain is installed.

I believe he may want to add or subtract about 1/2 and inch from that 31" C-T-C spec so your spindle will fall more in the middle vs. being biased well forward or well back of center.

If he keeps it at 31", you can adjust it back to center with a half-link in your sync chain, or you can bias your saddle fore-aft to adjust set-back and then establish your stem length for reach once you've got your set-back squared away.

This is why you'll find that most production tandems use the 1/2" spec on their boom tubes, e.g., 28.5" for Co-Motion, 27.5" for Santana, 28.6" for Cannondale, etc...
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Old 03-06-12, 05:17 PM   #42
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Ask your builder to check the boom tube length relative to where the front bottom bracket spindle will fall in the eccentric once the sync chain is installed.
Hi TG,

First let me say thanks for all that you have written about tandems. I've read lots both here on BF and on your blog.

With this design there is no eccentric BB. The tension in the timing chain is set by clamping the top tube in place, clamping one end of the boom tube, pressing down on the seat to tension the chain, and clamping the other end of the timing chain.
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Old 03-06-12, 05:20 PM   #43
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"You can see pictures of the tube in socket method applied to a recumbent tandem here. Bike Friday also uses this design on their tandems."

To be pedantic, while English is his own project, in effect he's also a major part of Bike Friday. I.E. I'd say that he's using the bikefriday design, not the other way around.
You are correct. I should have worded my post differently.
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Old 03-06-12, 06:02 PM   #44
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With this design there is no eccentric BB.
Guess I should have read with a more critical eye. I will be interested to hear how this works out.
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Old 03-09-12, 08:57 AM   #45
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Had no idea English was involved with Bike Friday.

I can remember getting passed one day in Central Park by a guy on a Bike Friday travel bike. The guy was flying, and the bike was really somethin' else. High zoot, tricked out, etc. Pretty darned cool machines.

I'm really interested in seeing how this all comes together. English def. thinks far outside the box with some of his designs.

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"You can see pictures of the tube in socket method applied to a recumbent tandem here. Bike Friday also uses this design on their tandems."

To be pedantic, while English is his own project, in effect he's also a major part of Bike Friday. I.E. I'd say that he's using the bikefriday design, not the other way around.
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Old 03-09-12, 11:14 AM   #46
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Having thought about your design a little more, and in light of the question regarding shifting performance in your original post, the only thing that comes immediately to mind is that you'll need to adjust your derailleurs after you've pre-loaded your sync chain vis-a-via the slip fitting of the boom tube into the socket clamps since the length of your tandem's mid-span will be somewhat 'variable'. In this regard, the new wireless shfting from Campy and Shimano would be a beautiful thing for this one-off design.

Again, I eagerly await its completion, photos and your ride reports.
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Old 03-09-12, 11:55 AM   #47
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Here's a photo of an English's recumbent tandem. That took some serious thinking for a one-off. Wow.

http://www.englishcycles.com/customb...em-recumbent/#


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Old 03-09-12, 06:46 PM   #48
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... the only thing that comes immediately to mind is that you'll need to adjust your derailleurs after you've pre-loaded your sync chain vis-a-via the slip fitting of the boom tube into the socket clamps since the length of your tandem's mid-span will be somewhat 'variable'.
Rob says that with a little practice you can get it so the mid-span doesn't vary from assembly to assembly. However, I expect to have to make a minor tweak to the derailleurs after each assembly.

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In this regard, the new wireless shfting from Campy and Shimano would be a beautiful thing for this one-off design.
I totally agree! I'm hopeful that one of the two will eventually produce a triple FD, but don't expect it for a couple more years. I figure that Shimano will be working on Di2 for mountain bikes next. Hopefully that will push them to develop a triple FD.

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Again, I eagerly await its completion, photos and your ride reports.
Me too!!!
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Old 03-11-12, 06:22 PM   #49
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I wanted to apologize if that came off as sharp / snippy, I was trying to go for clarification per-se.
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Old 03-11-12, 06:27 PM   #50
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I live in Portland, and due to geographic realities, there are a number of Bike Friday's on the road. I would find myself being passed by a mom riding a triplet & tag-along (so 3 kids) for a few years while commuting to and from work. Finally, just because it always tickled my fancy whenever I saw it, a former mayor (Bud Clark) would often be seen riding his bikefriday around town.
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